P-type nickel oxide deposited by reactive hollow cathode gas flow sputtering for the potential usage in thin-film transistors

Thin Nickel Oxide film were deposited by reactive pulsed-direct current hollow cathode gas flow sputtering. This unique technique allows for sputtering magnetic target materials with very high rates without magnetron. Deposition was carried out from a nickel target at room temperature. The influence of process parameters on optical, electrical, and structural film properties are investigated. High deposition rates of 6 nm/s and 2 nm/s are achieved for both direct current and pulsed-direct current power supply. All films are highly resistive and show p-type conduction that is tunable with oxygen flow. The films exhibit optical band gap around 3,8 eV depending on process parameters like oxygen flow and pulsing parameter. Secondary electron microscopy shows pillar-like growth perpendicular to the surface, while grazing incidence X-ray diffraction reveals smaller, randomly oriented crystals. Electrical properties of the films were tested by Hall measurements, revealing mobilities in the range of 1 cm2Vs. The nano crystalline thin films were tested in staggered bottom gate Thin-Film Transistor structures for potential use as channel layer. •Nickel oxide deposited by reactive hollow cathode gas flow sputtering.•Deposition rates from 2 nm/s to 6 nm/s have been achieved.•Contamination and magnetron free process from metallic target.•Electrical properties of p-type nano crystalline transparent films depend on oxygen flow.